The disclosure relates to alkali aluminosilicate glasses that have low softening points. More particularly, the disclosure relates to such glasses that are ion exchangeable and formable into three-dimensional shapes.
Ion exchangeable glasses are widely used as cover glass for displays found in many modern electronic devices, including hand-held devices. However, the use of these chemically-strengthenable glasses in such applications has been limited to devices that are, for the most part, flat and planar. The formation of three-dimensional (3D) glass shapes is sometimes achieved by molding and/or sagging process in which the glass is heated and allowed to sag under gravity or vacuum into a mold to obtain its final or near-final shape. Many ion-exchangeable glasses, however, have softening points that are so high that they tend to react with, stick to, and/or degrade the molds used for the sagging process, even when a protective mold coating is employed.
Lithium-containing alkali aluminosilicate glasses tend to have lower softening points, but limit the ion exchange properties of the glass when sodium in the glass is exchanged for potassium in the ion exchange medium. In order to achieve the desired depth of the resulting compressive layer (depth of layer, or DOL), such glasses must typically be ion exchanged at higher temperatures and for longer times which, from a manufacturing standpoint, are not practical or desirable. In addition, the level of compressive stress (CS) decreases with longer ion exchange times. Even when ion exchanged for long periods of time, the depth of the compressive layer tends to be relatively shallow.